This invention relates to the encasement of electrical circuits having a plurality of transformers, and more specifically relates to embedding or potting such electrical circuits in a housing of a dielectric material. Furthermore, this invention relates to an improvement over the invention disclosed in our previously-filed application, Ser. No. 07/935,549, filed Aug. 26, 1992, which disclosure is hereby incorporated by reference herein.
As stated in earlier application, Ser. No. 07/935,549 (hereinafter the "'549 invention"), many transformers have cores which are toroid or balun shaped because of their capability of performing well in a large bandwidth and their ability to confine substantially all of the magnetic field within the toroid or balun itself. Not only is this efficient, but the confining of the electromagnetic field prevents undue electromagnetic interference to surrounding elements near the transformer. Preventing such interference is particularly important when the surrounding elements are themselves electromagnetic in nature. Thus, it is advantageous to prevent interference between transformers in the same circuit.
However, it is often difficult to affix a toroid structure transformer to a circuit board or other mounting means because it has no flat edges. A balun structure is also difficult to mount as well if the windings are disposed upon the only flat surfaces. Additionally, once a toroid or balun transformer is in place, its shape causes its point of connection with the circuit board to be mechanically unstable.
Arrangements have been proposed for preventing electromagnetic interference between elements. Hassel, U.S. Pat. No. 2,021,060, discloses that for the various transformers in each stage of an amplifier, it is desirable to avoid the electromagnetic coupling caused by leakage lines of force between the different transformers in the different stages. Hassel teaches that two well known ways of preventing such electromagnetic coupling are to shield the transformers or arrange their axes at right angles to each other. Other references which disclose shielding the transformers of different stages include Braden, U.S. Pat. No. 2,065,884, and Wheeler, U.S. Pat. No. 2,075,683.
The prior U.S. patent application, the '549 invention, discloses particularly advantageous transformer circuit arrangements which solve the above problems such as preventing unwanted electromagnetic coupling between transformers. Despite the '549 invention, however, there is still a present need to provide greater electrical insulation and protection from unwanted interference, particularly in extremely compact circuits having interactive electrical components such as transformers mounted in close proximity to one another, including the circuits described in the '549 invention. Moreover, it is desirable to provide increased insulation and mechanical stabilization to the circuit at a low cost without complicated and expensive circuit enclosure or shielding techniques.
There is also a need to solve sealing problems associated with such transformer circuits which are sometimes enclosed within a metallic cover that is soldered to the mounting or circuit panel. For such transformer circuits requiring a soldered seal between the mounting and the cover, unwanted solidification of molten solder in the form of small balls inside the enclosed circuit is a great concern to component manufacturers. Namely, while still in a molten state, solder applied to seal the cover to the mounting can inadvertently enter or leak into the inside of the enclosure through space between the cover and the mounting. This can occur, for example, when the solder does not adhere to the metallic surfaces because of dirt particles or from uneven heat distribution. Component manufactures are in a constant effort to overcome this solder ball problem.
Furthermore, it is also desirable to provide increased physical stability to the electronic components and wiring that comprise the circuit, for example in plural transformer circuits such as those disclosed in the '549 invention, where the transformers themselves may be partially affixed to a circuit board or mounting. Thus, the planar base of a transformer having a cylindrical elongated core may be attached to a circuit panel, although still further physical stabilization and protection from accidental movement or dislodgement would be desirable.
Moreover, especially in plural transformer circuits utilizing toroid or balun shaped transformers, it would be desirable to increase the stability of such transformers when disposed on the circuit panel to overcome the mounting difficulties associated therewith as described above.
It is further desirable in such plural transformer circuits, regardless of whether elongated, toroid or balun shaped cores are employed, to provide relatively inexpensive shielding utilizing fewer manufacturing steps. Such shielding should be provided not only between the transformers themselves, but to the entire circuit so as to insulate the circuit from surrounding components or other objects capable of generating unwanted interference.
In this regard, further improvements in the encasement of such plural transformer circuits are needed.